Research On A Family Of High Frequency Modified SEPIC Converter Topologies And Its Key Technologies Based On GaN Device

As a new kind of green lighting source,light emitting diode(LED)has been widely used in lighting,TV liquid crystal display,signal display and other fields,among which automotive lighting is one of the important application fields.In recent years,with the maturity of the third generation of wide band gap semiconductor devices such as gallium nitride(Ga N),high frequency and high power density become the main development direction of power electronic converters.However,high switching loss,high drive loss and high magnetic loss caused by high frequency restrict the increase of switching frequency.This paper conducts in-depth research on key technologies such as topological structure of high-frequency and high-voltage gain vehicle-mounted LED drivers,resonant driver design and magnetic component optimization design method.The main research contents are as follows:The main high step-up technology represented by cascaded converter,switching capacitor,coupled inductor,etc.,mainly focuses on the step-up capacity of the converter,but cannot consider the problem of loss increase under the condition of high frequency application,which restricts the improvement of system efficiency.In order to solve the above problems,a family of quasi-resonant modified single ended primary inductor converters(SEPIC)suitable for high frequency conditions is proposed.Based on the traditional SEPIC converter structure,a series of high step-up units are integrated to obtain higher voltage gainy and lower voltage stress.Combined with soft switching technology,the resonant network is introduced,so that the converter has ZVS soft switching characteristics,and the efficiency under high frequency condition is increased.The working mechanism and parameter design method of passive components are studied,and the critical condition of soft switching is analyzed.Because the switches in the proposed converters work in quasi-resonant state,the traditional SEPIC converter control method and the existing hybrid control method are not suitable.To solve this problem,in this paper,a hybrid control method of changing the switching frequency and duty ratio simultaneously proposed.According to the relationship between the output voltage of the converter and the switching frequency and duty ratio,the switching frequency and duty ratio are directly adjusted at the same time,which increases the range of soft switching and improves the efficiency of the system.Based on the proposed topology family of quasi-resonant modified SEPIC converter,the efficiency improvement method of its drive circuit is further studied.The traditional driving circuit has the problems of large loss and limited driving speed in high frequency applications,so the resonant driving circuit is used in high frequency applications.Aiming at the classical current source resonant drive circuit,this paper compares the loss of the drive circuit under different driving modes,combined with device parameters,and determines the applicable occasions of each working mode.At the same time,as Ga N device is different from silicon device,and its opening threshold voltage is relatively low,which is susceptible to oscillation in the circuit.Besides,as there is no body diode of Ga N devices,the inverse conduction voltage drop is large.Hence,the conventional resonant drive circuit is not suitable for Ga N devices.To solve this problem,a resonant gate driver with asymmetrical voltage based on voltage shift circuit is proposed,the turn on and turn off voltages can be adjusted by changing the resistance in the voltage shift circuit to meet the operating characteristics of Ga N devices.The influence of resonance parameters on the characteristics of soft switching is analyzed,and an optimized design method of resonance parameters is established.In high frequency applications,magnetic components require small inductance.In this paper,planar magnetic components widely used in high frequency converters are adopted,which have the advantages of flat profile,good heat dissipation and easy repeat winding.In traditional method,interleaved structure is used to reduce leakage inductance of planar transformer but increase parasitic capacitance at the same time.Meanwhile,the loss of magnetic components increases greatly with the increase of switching frequency.To solve the above problems,this paper proposes a magnetic component optimization design method based on partially interleaved structure and decoupled integration.Partially interleaved structure reduces leakage inductance and parasitic capacitance parameters,and decoupled integration method reduces the number of magnetic elements in the converter and reduces the cost.Compared with different integration schemes,the influence of the proposed magnetic integration method on the efficiency of the converter is analyzed and the optimized magnetic integration structure is designed.At the same time,the modeling method of magnetic resistance and inductance of planar magnetic components is deduced,and compared with the simulation results,the accuracy of the above theoretical analysis is verified.On the basis of system steady state analysis and further improve the dynamic performance of the proposed converter,the generalized state space average modeling method is used to establish a small signal model for the converter with resonance mode.According to the small signal model,the open-loop transfer function of the system output to the control variables is derived,the Bode diagram is drawn,and the high-order compensator is designed to improve the dynamic performance of the system.In this paper,an experimental prototype with rated output power of 36 W and rated switching frequency of 1 MHz is designed and manufactured.The experimental results are consistent with the theoretical analysis,which verifies the correctness of the theoretical research.